1. Field of the Invention
The invention relates to sampling chemical-mechanical polishing slurries. In one aspect, the invention relates to sampling such slurries to monitor one or more properties of the slurry while in another aspect, the invention relates to using an aspirator to draw the slurry into a liquid sampling system.
2. Description of the Related Art
A chemical-mechanical polishing (CMP) system is often employed in the microelectronics industry to contour and/or polish semiconductor wafers. These systems typically contain and employ a xe2x80x9cslurryxe2x80x9d which is cycled throughout the system such that the slurry contacts and/or impinges upon the wafers. As the cycling slurry impacts and/or passes over the wafers, the wafers are contoured and polished.
In order to maintain the consistency, performance, efficiency, and/or usefulness of the system, the xe2x80x9chealthxe2x80x9d of the slurry must be maintained. Slurry instability, external contamination, or process conditions (e.g., shear-inducing pressure gradients, flow rates, and exposure to air) may all compromise slurry health. Thus, slurry properties (e.g., specific gravity, pH, weight percent solids, ionic contamination level, zeta potential, and particle size distribution (PSD)), are often closely monitored by sampling systems.
Of all the slurry health properties, perhaps the most important and frequently monitored is PSD. In the industry, PSD can be observed using a variety of instruments such as sensors, analyzers, and like devices (collectively referred to as sensors) that are commercially available from a host of manufacturers. For example, one such sensor is the AccuSizer 780/OL (AccuSizer) manufactured by Particle Sizing Systems (PSS) of Santa Barbara, Calif.
Unfortunately, while these PSD sensors are generally suitable for analyzing slurry, these sensors can possess disadvantages in some circumstances. Certain of these sensors are generally limited to sampling a single slurry at a single sampling point (i.e., a location within a CMP system from where a sample is taken). In other words, each CMP system, as well as each slurry used within that CMP system, would require a dedicated sensor. Since integrated circuit manufacturers, as well as others, often desire to analyze numerous different slurries, from multiple sampling points (i.e., locations), a one-to-one ratio of sensor to slurry would dramatically increases costs. Therefore, a liquid sampling system, using a single sensor, capable of monitoring one of a plurality of slurries from multiple sampling points was developed.
The liquid sampling system was built around a sensor to permit measurement of a number of different slurries, from multiple sample points, by utilizing a multi-port valve manifold. The multi-port valve manifold is operable, within the liquid sampling system, to selectively route any one of a number of different slurries, from a variety of locations, to a single sensor for PSD analysis.
While developing, testing and using the liquid sampling system, the need to repeatedly draw and/or introduce the slurry into the liquid sampling system became apparent. The slurries could, and often were, provided by one of many independent slurry supply lines. Therefore, in order to draw slurry into the liquid sampling system, a pump or like device would need to be associated with every slurry supply line. In other words, a one-to-one ratio of slurry supply lines to pumps would be required.
Unfortunately, the use of multiple pumps within the liquid sampling system presented numerous drawbacks and disadvantages. Specifically, the cost of purchasing, maintaining, and operating numerous pumps posed a significant financial burden. The pumps can be expensive, can be subject to mechanical difficulties that lead to down-time, and can voraciously consume energy. Further, the pumps can occupy valuable space within the liquid sampling system and, therefore, render the liquid sampling system cumbersome. Thus, an apparatus and method capable of drawing a liquid into a liquid sampling system without the use of multiple pumps or other multiple drawing apparatus are desirable.
In one aspect, the invention is a method of drawing a liquid sample into a liquid sampling system from at least one of a plurality of liquid delivery lines, the liquid sampling system comprising (i) a multi-valve manifold in fluid communication with the liquid delivery lines, (ii) an aspirator in fluid communication with the manifold, and (iii) a pressure between the aspirator and the liquid delivery lines, the method comprising:
activating the aspirator to reduce the pressure in the manifold relative to the liquid delivery lines; and
activating at least one valve on the manifold to selectively draw into the manifold a liquid sample from at least one liquid delivery line.
The aspirator is activated by passing a fluid, e.g., water, through it, and the liquid sample is typically a chemical-mechanical polishing slurry.
In another embodiment, the invention is an apparatus for drawing a sample of a chemical-mechanical polishing slurry for analysis of at least one property, the apparatus comprising (i) a plurality of sample delivery lines, each line carrying a chemical-mechanical polishing slurry, (ii) a manifold in fluid communication with the plurality of sample delivery lines, (iii) means for opening and closing the fluid communication between each sample delivery line and the manifold, (iv) an aspirator in fluid communication with the manifold, (vi) means opening and closing the fluid communication between the aspirator and the manifold, (vii) a pressure between the aspirator and the sample delivery lines, a reduction in the pressure resulting in the draw of a sample from the sample delivery line into the manifold when the fluid communication between the line and the manifold is open, (viii) a sensor for measuring the at least one property of the slurry, the sensor in fluid communication with the manifold, and (ix) means for opening and closing the fluid communication between the manifold and the sensor.
The means for opening and closing the fluid communication between the manifold and the sample delivery lines, aspirator and sensor is typically at least one valve. The sensor can vary to convenience, e.g., an optical particle counter.